From US 2007 018 327 a method for measuring a surface of a component is known, which method uses the photogrammetry method and the laser-tracking method for measuring the surface. In the method disclosed in the aforesaid, a camera is moved along a path, wherein a multitude of images of the surface of a component are recorded from different angles of view. Furthermore, at each point in time of recording an image the position of the camera is recorded.
In this method in a first step a first set of measurement data is generated by measuring the surface with two cameras, wherein photogrammetry is used. In a second step a second set of measurement data is generated by measuring the surface with a laser tracker. In a third step the data for the camera positions is determined with the use of the laser tracker. Finally, the first set of measurement data and the second set of measurement data are superimposed together with the data relating to the camera position.
In addition to the method for measuring the surface of a component, the printed publication discloses a system for measuring the surface of a component. This system comprises a slide that moves along a path. On the slide, cameras are arranged so as to be fixed in position, which cameras on various positions along the path take images of the surface of the component. In addition, a projector and reflective targets are mounted on the slide, wherein the projector generates an illumination pattern on the surface of the component. The reflective targets are also mounted on the surface of the component, which surface is to be measured, and are used by the statically held laser tracker for measuring the position of the surface of the component, and for measuring the position of the slide at the point in time the respective image is taken.
The generally-known state of the art shows that optical measuring methods based on image processing are used for measuring displacements and deformations. In these methods the object to be measured comprises suitable markings, and an optical structure for taking images with cameras that are positioned so as to be fixed relative to each other. The accuracy of the measuring results depends on this optical design, the nature of the object markings and the illumination conditions. At present there is no calibration method that takes into account these factors of influence.
In the hitherto-used calibration methods a measuring arrangement is produced in a calibration laboratory. Subsequently, calibration objects are measured. This method is associated with disadvantages in that, on the one hand, the setup in the laboratory takes place under ideal conditions so that the calibration setup usually has more favorable characteristics than a real measuring arrangement, and, on the other hand, most of the time the calibration objects do not cover the entire possible measuring volume.